With all these success stories about people feeling better on various diets, I think we forgot the people who sometimes feel worse. Probably because those people give up and don't stick around. I'm known many people who have adopted paleo, primal, ancestral, low-carb, gluten-free, or whatever diet. And instead of feeling better, they have all kinds of problems, particularly stomach problems.

There are many reasons why this happens, here are a couple I tend to come across:

1. They hose their digestive system with "cleanses." For example, the Master Cleanse, which involves fasting on just lemon juice, maple syrup, and cayenne for a few days to a week. Now I love spicy food. And I love acidic food. But out of the context of real whole meals, there is plenty of evidence they can be irritants, particularly in the digestive lining. There is no evidence that the Master Cleanse will remove some nebulous "toxins," but you are not only disturbing your gut microbiota (both good and bad) and irritating the mucous membranes of your gut, but also depriving yourself of real nutrients your body uses to maintain its defenses. You'll come out of it with possibly increased gut permeability and a devastated population of gut microbes. If you've already tormented your poor gut with this, you might need to eat a gentle diet (FODMAPS, for example) and take probiotics until your gut becomes less inflamed and repairs itself. People do often feel better on cleanses though in other ways, but that's because they are excluding many foods and yes, there is some value in breaking up pathogenic biofilms in the gut, but there are possibly more sustainable and gentle ways to do so based on preliminary scientific studies.

2. Speaking of FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. ), another reason people might feel worse is that many so-called safe or good foods on these diets are difficult for many people to digest. A lot of books talk about how difficult it is to digest grains, but many plants have similar complex carbohydrates that can cause gas, bloating, and other GI symptoms. Rice, for example, is mostly nutritionless, but has had most of its complex carbohydrates polished away. If you take it out of your diet and replace it with "grain-free cauliflower 'rice'", you are consuming a massive amount of Oligosaccharides. I personally had a lot of bloating from foods like this. Remove them from your diet and then add them back in slowly one at a time to see what you can tolerate.

3. They forget any food can be toxic. Gluten, for example, seems to take a beating in the "toxic" department with nearly every book talking about how bad it is and how many people have celiac, which shows how gluten is a terrible non-food that no one should ever eat. But plenty of people are allergic to shrimp and we don't talk about how we aren't meant to eat shrimp because of that. I also see people talking about toxic lectins and phytic acid, but these aren't just in grains, they can be in any plant food. Peanuts and gluten are particularly bad because their biochemical structure causes problems for many people, but you can be sensitive to any food. Even beef. Once you take off the blinders, maybe you should consider whether or not you are feeling sick because a "safe" food isn't so safe for you? Or maybe you shouldn't be eating bread made out of an entire cup of walnuts, which might overload the capacity of your body to deal with the phytic acid and other assorted irritants in nuts.

4. They think fermented foods are always good. Sauerkraut? It's a cure-all! Why not eat it with every meal? Unfortunately, we do not have the robust digestive systems of our ancestors. If your gut is damaged, contamination of fermented foods by mold or sensitivity to histamine can be a real issue. You might have to remove them from your diet or at least find a source that is less likely to be contaminated. Additionally, fermentation does not always remove all FODMAPs, so many FODMAPs sensitive people will have digestive symptoms when eating things like sauerkraut.

5. They put massive amounts of fat on top of everything. So you heard fat has been unfairly maligned? Time to put massive amounts of coconut oil, butter, coconut milk, lard, and other fats on top of all your food right? Well, maybe slow down a bit and give your body some time to adjust to a higher-fat diet before you make your diet mostly fat, because adding in it all at once all the sudden can cause GI problems. For a long time I was one of those people who thought that only carbohydrates could cause GI symptoms and contribute to dysbiosis, but fat definitely can increase levels of endotoxins and increase gut permeability as well, and it seems that phytochemicals may inhibit that process. So, instead of chugging that can of coconut milk before your workout, maybe consider having a normal meal that includes a variety of other foods as well. In the end, while it might sound like heresy, some people actually might not do very well on high-fat diets. Try replacing processed carb foods in your regular diet with fruits and tubers instead of with fatty foods.

6. They take massive amounts of supplements. When you are taking ten different supplements, the odds that you are taking one that is irritating your stomach get pretty high. Mineral supplements like magnesium and iron are top offenders, as are supplements that contain FODMAPs in the form of prebiotics like inulin. Stop taking the supplements until your stomach sorts out and then add them back in one at a time to see which ones you can tolerate. With iron, it is probably advisable to get it from food, since excess iron can feed pathogenic gut bacteria.

7. Undereating can be just as problematic as overeating, particularly on a new diet. If you undereat, your body won't be able to maintain its systems effectively, which can make your digestive system prone to irritation. Counting calories may not be perfectly accurate, but it can help you get an idea of whether or not you aren't giving your body enough nourishment.

8. Excessive amounts of protein all at once. One friend recently told me he was having stomach problems on paleo. Turns out he was mainly eating chicken , which was providing massive amounts of protein without much fat, probably leading to a type of mild "rabbit starvation." As arctic explorer Vilhjalmur Stefansson wrote:

But it has been found in various parts of the world that a diet of lean meat exclusively will cause diarrhea in from three days to a week. If no fat can be added to the lean, the diarrhea becomes serious and will lead to death. A well known field where such deaths occur is the northern edge of the forest in Canada where Indians are sometimes unable to find any food except rabbits. The expression "rabbit starvation," frequently heard among the Athapsc Indians north-west of Great Bear Lake, means not that people are starving because there are no rabbits but that they are going through the experience of starvation with plenty of rabbit meat. For this animal is so lean that illness and death result from being confined to its flesh.

in this situation, it would be wise to add some fat, carbohydrate, or both to the diet to normalize things. You might be able to tolerate higher protein if you add it in slowly. You are probably not going to die, it's more likely you will discontinue the diet when your roommate orders pizza and you feel better after a few slices.

9. They have food poisoning. I'll never forget several years ago in college when I was having worsening IBS symptoms and I kept trying to fix them with diet until I ended up in the ER. A stool culture revealed I had salmonella and needed antibiotics. If you symptoms keep getting worse, it might be time to go to the doctor and ask for a stool culture.

10. These diets can't fix everything. I know several people for whom no dietary tweaking worked and they were later diagnosed with serious IBD. They are doing better on medicine. In the old days, they probably would have died. Many many people died in the past from diarrhea. Don't beat yourself up if you can't eat your way out of a very serious illness. Some people can, some people can't. Modern medicine can make your life better if you are one of the latter. Even if you don't have a serious stomach disorder, there are tons of non-diet things that can cause stomach problems, like sleeping poorly or thyroid conditions.